With advancements in technologies, demands for higher quality and larger size of video frame continue to increase as resolution, specification and size of a video display becomes higher. To satisfy the demands, Joint Collaborative Team on Video Coding (JCT-VC) co-founded by Video Coding Experts Group (VCEG) under ITU-T (International Telecommunication Union Telecommunication Standardization Sector) and Moving Picture Experts Group (MPEG) under ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission) has started to work on H.265/HEVC (High Efficiency Video Coding) project which aims to provide an encoding efficiency higher than that of a video compression standard of H.264/AVC (Advanced Video Coding). The project is important for high resolution videos such as HD (High Definition), Ultra HD (Ultra High Definition), and the like.
An environment for such video application in large size and high resolution mostly include natural video images and was finalized in 2013. Currently, the HEVC SCC (Screen Content Coding; SCC) standard is under establishment. A video content for screen sharing usually includes a hybrid video content material. For example, a frame may include a natural image, a massive amount of text, a mouse pointer, or various lines, etc. Because this screen application environment is different with the target designed by H.265/HEVC, JCT-VC has recently changed its focus onto developments for new screen coding standard technology with higher performance. SCC standard is developed based on existing tools of H.265/HEVC. For example, a palette mode is an encoding technology for the SCC standard. Technical concepts of the palette mode includes searching for one or more major colors to represent pixels within a coding unit (CU) block currently under encoding, and using indexes corresponding to the major colors to perform index numbering for pixels within the coding unit block. An encoding end establishes an index map by using the indexes corresponding to the major colors, and transmits the one or more major colors and the indexes corresponding to colors of the pixels in the index map to a decoding end.
However, in order to maintain the flexibility in the encoding computation, one index is reserved for specific pixels not represented by the major colors in the coding unit block in the palette mode. Said specific pixels are known as escape pixel(s), and the reserved index is known as an escape index. In view of the above, it can be known that in a transmitting process in the palette mode, the transmitted indexes include the indexes of the major colors and the escape index. Therefore, in the case where the coding unit block currently under encoding does not include the escape pixel, preservation of the escape index can cause an unnecessary burden in transmission of the indexes of the coding unit block.